U.S. patent number 9,221,149 [Application Number 14/249,377] was granted by the patent office on 2015-12-29 for method for polishing semiconductor wafers by means of simultaneous double-side polishing.
This patent grant is currently assigned to SILTRONIC AG. The grantee listed for this patent is Siltronic AG. Invention is credited to Rainer Baumann, Alexander Heilmaier, Leszek Mistur, Klaus Roettger, Johannes Staudhammer.
United States Patent |
9,221,149 |
Baumann , et al. |
December 29, 2015 |
Method for polishing semiconductor wafers by means of simultaneous
double-side polishing
Abstract
A method of polishing a semiconductor wafer includes
simultaneous double-side polishing the wafer in a gap of a
polishing device between a lower polishing plate covered with a
lower polishing pad and upper polishing plate covered with an upper
polishing pad while supplying a polishing agent. A first of the
upper and lower polishing pads is dressed using a dressing tool.
The dressing tool is mounted in the gap so that it extends from the
inner edge to the outer edge of the first polishing pad. The
distance between the dressing tool and a second of the upper and
lower polishing pads at the inner edge of the second polishing pad
differs from a corresponding distance at the outer edge of the
second polishing pad. After the dressing, the at least one
semiconductor wafer in the gap is polished.
Inventors: |
Baumann; Rainer (Burghausen,
DE), Staudhammer; Johannes (Burghausen,
DE), Heilmaier; Alexander (Haiming, DE),
Mistur; Leszek (Burghausen, DE), Roettger; Klaus
(Bachmehring, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Siltronic AG |
Munich |
N/A |
DE |
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Assignee: |
SILTRONIC AG (Munich,
DE)
|
Family
ID: |
51618384 |
Appl.
No.: |
14/249,377 |
Filed: |
April 10, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140308878 A1 |
Oct 16, 2014 |
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Foreign Application Priority Data
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Apr 12, 2013 [DE] |
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10 2013 206 613 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B
53/017 (20130101); H01L 21/304 (20130101); B24B
37/08 (20130101) |
Current International
Class: |
B24B
37/08 (20120101); H01L 21/304 (20060101); B24B
53/017 (20120101) |
Field of
Search: |
;451/56,57,443 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102010032501 |
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Feb 2012 |
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DE |
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2007118146 |
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May 2007 |
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JP |
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2010128631 |
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Nov 2010 |
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WO |
|
Primary Examiner: Nguyen; George
Attorney, Agent or Firm: Leydig, Voit & Mayer, Ltd.
Claims
What is claimed is:
1. A method of polishing at least one semiconductor wafer in a gap
of a polishing device between a lower polishing plate, covered with
a lower polishing pad, and an upper polishing plate, covered with
an upper polishing pad, while supplying a polishing agent, the
polishing plates and the polishing pads having an inner edge and an
outer edge, the method comprising: dressing a first of the upper
and lower polishing pads using a dressing tool, the dressing
including rotating the respective polishing plate covered with the
first polishing pad, the dressing tool being mounted in the gap in
such a way that it extends from the inner edge to the outer edge of
the first polishing pad, and a distance between the dressing tool
and a second of the upper and lower polishing pads at the inner
edge of the second polishing pad differing from a corresponding
distance at the outer edge of the second polishing pad; and
simultaneous double-side polishing the at least one semiconductor
wafer in the gap after the dressing.
2. The method as recited in claim 1 further comprising dressing the
second polishing pad subsequent to the dressing of the first
polishing pad.
3. The method as recited in claim 1, wherein one or more polishing
methods are carried out before the at least one polishing pad
undergoes subsequent dressing.
4. The method as recited in claim 1, wherein the dressing imparts a
profile to the gap between the upper and lower polishing pads such
that a width of the gap at the inner edge of the polishing pads is
greater than the width of the gap at the outer edge of the
polishing pads.
5. The method as recited in claim 1, wherein the dressing tool
comprises one or more rings, which are placed between an inner and
an outer drive gear of the polishing device and are set in rotation
about the middle of the ring by one of the inner drive gear, the
outer drive gear, or both the inner and outer drive gears.
6. The method as recited in claim 4, wherein the profile is thinner
at the inner edge than at the outer edge.
7. The method as recited in claim 4, wherein an amount of
difference in widths of the gap is in a range of from 10 to 250
.mu.m.
8. The method as recited in claim 4, wherein an amount of
difference in widths of the gap is in a range of from 30 to 150
.mu.m.
9. A method for a polishing semiconductor wafer via simultaneous
double-side polishing in a gap between a lower polishing pad,
disposed on a lower polishing plate, and an upper polishing pad,
disposed on an upper polishing plate, of a polishing device while
supplying a polishing agent, the polishing plates and the polishing
pads having an inner edge and an outer edge, the method comprising:
dressing, with a dressing tool, the lower polishing pad while
rotating the lower polishing plate, the dressing tool being mounted
in the gap in such a way that the dressing tool extends from the
inner edge to the outer edge of the lower polishing pad; and, after
the dressing, double-side polishing the semiconductor wafer in the
gap, wherein, during the dressing, a distance of the dressing tool
from the upper polishing pad, at the inner edge of the upper
polishing pad, differs from a distance at the outer edge of the
upper polishing pad.
10. The method as recited in claim 9, further comprising, before
the double-sided polishing, but subsequent to the dressing of the
lower polishing pad: dressing the upper polishing pad.
11. The method as recited in claim 9, wherein one or more polishing
methods are carried out before the at least one polishing pad
undergoes subsequent dressing.
12. The method as recited in claim 9, wherein the dressing imparts
a profile to the gap between the upper and lower polishing pads
such that a width of the gap at the inner edge of the polishing
pads is greater than the width of the gap at the outer edge of the
polishing pads.
13. The method as recited in claim 9, wherein the dressing tool
comprises one or more rings, which are placed between an inner and
an outer drive gear of the polishing device and are set in rotation
about the middle of the ring by one of the inner drive gear, the
outer drive gear, or both the inner and outer drive gears.
14. The method as recited in claim 12, wherein the profile is
thinner at the inner edge than at the outer edge.
15. A method for a polishing semiconductor wafer via simultaneous
double-side polishing in a gap between a lower polishing pad,
disposed on a lower polishing plate, and an upper polishing pad,
disposed on an upper polishing plate, of a polishing device while
supplying a polishing agent, the polishing plates and the polishing
pads having an inner edge and an outer edge, the method comprising:
dressing, with a dressing tool, the upper polishing pad while
rotating the upper polishing plate, the dressing tool being mounted
in the gap in such a way that the dressing tool extends from the
inner edge to the outer edge of the upper polishing pad; and, after
the dressing, double-side polishing the semiconductor wafer in the
gap, wherein, during the dressing, a distance of the dressing tool
from the lower polishing pad, at the inner edge of the lower
polishing pad, differs from a distance at the outer edge of the
lower polishing pad.
16. The method as recited in claim 15, further comprising, before
the double-sided polishing, but subsequent to the dressing of the
lower polishing pad: dressing the upper polishing pad.
17. The method as recited in claim 15, wherein one or more
polishing methods are carried out before the at least one polishing
pad undergoes subsequent dressing.
18. The method as recited in claim 15, wherein the dressing imparts
a profile to the gap between the upper and lower polishing pads
such that a width of the gap at the inner edge of the polishing
pads is greater than the width of the gap at the outer edge of the
polishing pads.
19. The method as recited in claim 15, wherein the dressing tool
comprises one or more rings, which are placed between an inner and
an outer drive gear of the polishing device and are set in rotation
about the middle of the ring by one of the inner drive gear, the
outer drive gear, or both the inner and outer drive gears.
20. The method as recited in claim 18, wherein the profile is
thinner at the inner edge than at the outer edge.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority from German Patent Application No
DE 10 2013 206 613.9 filed Apr. 12, 2013, which is hereby
incorporated by reference herein in its entirety.
FIELD
The invention relates to a method for polishing semiconductor
wafers by means of simultaneous double-side polishing in a gap
between a lower and an upper polishing pad of a polishing device
while supplying a polishing agent, the lower polishing pad covering
a lower polishing plate and the upper polishing pad covering an
upper polishing plate, and the polishing plates and the polishing
pads having an inner edge and an outer edge. The method comprises
dressing of one or both polishing pads with a dressing tool and
polishing of semiconductor wafers in the gap after the
dressing.
BACKGROUND
Semiconductor wafers, in particular semiconductor wafers of
monocrystalline silicon, are needed as basic materials for the
production of electronic components. The manufacturers of such
components require that the delivered semiconductor wafers have
front and back sides which are as far as possible planar and
parallel to one another. In order to meet this requirement, a
processing step for the production of such semiconductor wafers
conventionally comprises polishing thereof. Double-side polishing
(DSP), in which the front side and the back side of the
semiconductor wafer are simultaneously polished in the presence of
a polishing agent, is particularly suitable. During DSP, the
semiconductor wafer is located together with further semiconductor
wafers in a gap between a lower polishing pad and an upper
polishing pad. Each of the polishing pads covers a corresponding
lower and upper polishing plate. The semiconductor wafers lie
during the DSP in openings of carriers, which guide and protect
them. The carriers are externally toothed disks, which are arranged
between an inner and an outer toothed wheel or pin gear of the
polishing device. A toothed wheel or pin gear will be referred to
below as a drive gear. During polishing, the carriers are set in a
rotational movement about their middle and the middle of the
polishing plates by the inner drive gear or by the inner and outer
drive gears. Furthermore, the polishing plates are usually also
rotated in countersense about their axes, which results in
kinematics characteristic of DSP, in which a point on a
semiconductor wafer side to be polished follows a cycloid path on
the corresponding polishing pad.
Before first use and after a certain degree of wear is reached, it
is usual to dress the lower and upper polishing pads. During the
dressing, the surface of the polishing pad is roughened and slight
material abrasion is induced in order to impart a favourable
working state to the polishing pad.
According to U.S. Patent Publication No. 2012/0189777, it is
advantageous to subject the polishing plates to shaped dressing
("truing"), so that the gap between the polishing pads is as far as
possible uniformly wide. Furthermore, it is described therein that,
in order to dress the polishing pads, the carriers are replaced by
dressing rings. The dressing is carried out in the presence of a
cooling lubricant, the dressing rings being moved over the lower
and upper polishing pads, in the absence of inserted semiconductor
wafers, in a movement similar to the kinematics of the DSP.
SUMMARY
In an embodiment, the present invention provides a method of
polishing at least one semiconductor wafer including simultaneous
double-side polishing the at least one wafer in a gap of a
polishing device between a lower polishing plate covered with a
lower polishing pad and upper polishing plate covered with an upper
polishing pad while supplying a polishing agent. The polishing
plates and polishing pads have an inner edge and an outer edge. A
first of the upper and lower polishing pads is dressed using a
dressing tool. The dressing includes rotating the respective
polishing plate covered with the first polishing pad. The dressing
tool is mounted in the gap in such a way that it extends from the
inner edge to the outer edge of the first polishing pad. The
distance between the dressing tool and a second of the upper and
lower polishing pads at the inner edge of the second polishing pad
differs from a corresponding distance at the outer edge of the
second polishing pad. After the dressing, the at least one
semiconductor wafer in the gap is polished.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described in even greater detail
below based on the exemplary figures. The invention is not limited
to the exemplary embodiments. All features described and/or
illustrated herein can be used alone or combined in different
combinations in embodiments of the invention. The features and
advantages of various embodiments of the present invention will
become apparent by reading the following detailed description with
reference to the attached drawings which illustrate the
following:
FIG. 1 shows a sectional representation of an arrangement of the
dressing tool during the dressing of a polishing pad according to
the first embodiment of the invention.
FIG. 2 shows the arrangement according to FIG. 1 in a plan view of
the polishing pad lying opposite the polishing pad to be
dressed.
FIG. 3 shows a sectional representation of an arrangement of the
dressing tool during the dressing of a polishing pad according to
the second embodiment of the invention.
FIG. 4 shows the arrangement according to FIG. 3 in a plan view of
the polishing pad lying opposite the polishing pad to be
dressed.
FIG. 5 shows a sectional representation of an arrangement of
semiconductor wafers during DSP in a gap having a wedge-shaped
profile.
DETAILED DESCRIPTION
An aspect of the present invention is to provide an approach which
leads to an improvement in the planarity of the semiconductor
wafers after DSP has been carried out.
In an embodiment, the present invention provides a method for
polishing semiconductor wafers by means of simultaneous double-side
polishing in a gap between a lower and an upper polishing pad of a
polishing device while supplying a polishing agent, the lower
polishing pad covering a lower polishing plate and the upper
polishing pad covering an upper polishing plate, and the polishing
plates and the polishing pads having an inner edge and an outer
edge, comprising dressing of one, or first one and subsequently the
other, polishing pad with a dressing tool, the polishing plate
which is covered with the polishing pad to be dressed being rotated
and the dressing tool being mounted in the gap in such a way that
it extends from the inner edge to the outer edge of the polishing
pad to be dressed; and polishing of semiconductor wafers in the gap
after the dressing, characterized in that, during the dressing, the
distance of the dressing tool from the polishing pad lying opposite
the polishing pad to be dressed, at the inner edge of this
polishing pad, differs from the corresponding distance at the outer
edge of this polishing pad.
The inventors have discovered that in order to improve the
planarity, particularly in the edge region of the semiconductor
wafer, it is advantageous for the semiconductor wafer to be
subjected to DSP and in this case for the width of the gap to be
modified from the inner edge to the outer edge of the polishing
pads, instead of remaining the same. The width of the gap is the
distance between the lower and upper polishing pads. It preferably
varies linearly. The gap is preferably wider at the inner edge of
the polishing pads than at the outer edge of the polishing pads,
and accordingly has a profile with a wedge shape. The amount of the
difference in the width of the gap is from 10 .mu.m to 250 .mu.m,
preferably from 30 .mu.m to 150 .mu.m, when the width of the gap at
the inner edge of the polishing pads is compared with the width of
the gap at the outer edge of the polishing pads. The dressed
polishing pad is accordingly preferably thinner at the inner edge
than at the outer edge.
The favourable profile of a gap is achieved by dressing one or both
polishing pads with a dressing tool. If both polishing pads are
dressed, the lower or upper polishing pad is dressed first and the
polishing pad lying opposite the dressed polishing pad is
subsequently dressed.
The dressing tool preferably comprises a plurality of dressing
rings and particularly preferably three dressing rings, which are
placed instead of carriers between the inner and outer drive gears.
Each dressing ring has an upper side, facing toward the polishing
pad to be dressed, which is provided with grinding bodies. The
lower side lying underneath may likewise be provided with grinding
bodies. The grinding bodies contain abrasively acting material,
preferably grains of diamond, cubic boron nitride, corundum or
silicon carbide. The average grain size is preferably from 60 .mu.m
to 300 .mu.m.
The dressing tool extends from the inner edge to the outer edge of
the polishing pad to be dressed. According to an embodiment of the
invention, during the dressing, the distance from the dressing tool
to the polishing pad lying opposite the polishing pad to be dressed
is different at the inner edge of this polishing pad than the
corresponding distance at the outer edge of this polishing pad.
This is achieved by the dressing tool being mounted in such a way
that it is arranged tilted from a horizontal position. Preferably,
a spacer is placed between the dressing tool and the polishing pad
lying opposite the polishing pad to be dressed. The distance
between the dressing tool and the polishing pad lying opposite the
polishing pad to be dressed is greater at the inner edge of this
polishing pad than at the outer edge of this polishing pad. This is
the distance between the dressing tool surface formed by the
grinding bodies and the surface of the polishing pad lying opposite
the polishing pad to be dressed.
According to one embodiment, the spacer comprises one or more rings
which bear on the polishing pad lying opposite the polishing pad to
be dressed. Such a spacer ring extends from the inner edge to the
outer edge of the polishing pad. At the inner edge of the polishing
pad, it has a thickness which is preferably greater than its
thickness at the outer edge of the polishing pad. The dressing tool
bears on the spacer in the region of the inner and outer edges of
the polishing pad. Accordingly, the distance between the dressing
tool and the polishing pad lying opposite the polishing pad to be
dressed is greater at the inner edge of this polishing pad than at
the outer edge of the polishing pad.
Preferably, three spacers are provided, which bear on the polishing
pad lying opposite the polishing pad to be dressed while being
uniformly distributed. The spacers are preferably connected to one
another by bars which act as security against twisting of the
spacers.
In order to dress a polishing pad, the polishing plates are closed,
and the polishing plate which is covered by the polishing pad to be
dressed is set in rotation. The other polishing plate is not
rotated. Furthermore, the dressing tool mounted according to an
embodiment of the invention is set in rotation about its own middle
with the aid of the inner or outer drive gear or with the aid of
both. The upper polishing plate is universally suspended, in order
to permit relative movement of the dressing tool and the polishing
plate in motion, as a result of which the polishing pad to be
dressed is processed over its full surface.
According to another embodiment, the spacer is a single ring which
bears on the polishing pad lying opposite the polishing pad to be
dressed. This spacer ring encloses the inner edge of the polishing
pad and the inner drive gear. The dressing tool bears on the spacer
in the region of the inner edge of the polishing pad and on the
polishing pad in the region of the outer edge of the polishing pad.
At the inner edge of this polishing pad, the distance between the
dressing tool and the polishing pad lying opposite the polishing
pad to be dressed is equal to the sum of the thickness of the
dressing tool and the thickness of the spacer. At the outer edge of
the polishing plate, the distance is less by the thickness of the
spacer.
The dressing is preferably carried out in the presence of a cooling
lubricant.
Following the dressing of one or both polishing pads, semiconductor
wafers lying in carriers are subjected to simultaneous double-side
polishing in the gap between the polishing pads, a plurality of
semiconductor wafers being polished simultaneously in one polishing
run. A plurality of polishing runs are carried out before one of
the polishing pads or both polishing pads are dressed according to
an embodiment of the invention once more. The subsequent dressing
can be obviated so long as the profile of the gap retains the
desired wedge shape. If the polishing no longer meets the
expectations placed on it in respect of the planarity of the
polished semiconductor wafers, owing to the nonuniform polishing
wear, the desired profile of the gap should be restored. In this
case, a further dressing cycle is carried out. The polishing pads
may possibly need to be replaced beforehand.
According to FIG. 1, the lower polishing plate 2 and the upper
polishing plate 1 extend radially from an inner edge to an outer
edge, as do the lower polishing pad 4 and the upper polishing pad
3, which cover the respective polishing plates. The lower polishing
pad 4 forms an annular surface which at the inner edge adjoins an
inner pin gear 6 of the polishing device and at the outer edge
adjoins an outer pin gear 7 of the polishing device. Three dressing
rings 11 are placed on the lower polishing pad 4 while being
uniformly distributed. They respectively bear on a spacer ring 14
made of plastic. The spacer rings have a wedge shape in cross
section. The spacer rings 11 extend from the inner edge to the
outer edge of the upper polishing pad 3 to be dressed, and have
teeth 12 on the circumference, which engage into the pins of the
inner and outer pin gears 6, 7.
The upper sides of the spacer rings 11 are provided with grinding
bodies 13. During the dressing of the upper polishing pad, the
upper polishing pad 3 (upon upper polishing plate 1) is rotated
about its rotation axis 5. The lower polishing pad 4 (upon lower
polishing plate 2) remains stationary during this. The distance
D.sub.i, between the lower polishing pad 4 and the spacer ring 11
at the inner edge of the polishing pad is greater than the
corresponding distance D.sub.o at the outer edge of the polishing
pad.
Owing to the wedge-shaped configuration of the cross section of the
spacer rings 14 with different thickness on the inner and outer
edges of the polishing pad 4, the spacer rings 11 assume an oblique
position relative to the horizontal during the dressing.
Accordingly, the material abrasion from the upper polishing pad 3,
induced during the dressing, is dependent on the radial position.
It decreases from the inner edge of the polishing pad to the outer
edge of the polishing pad.
If it is intended subsequently to dress the lower polishing pad 4
as well, the dressing rings 11 and the spacer rings 14 are rotated
through 180.degree. and arranged in the gap between the polishing
pads, and the lower polishing pad 2 is rotated instead of the upper
polishing pad 1 during the dressing.
FIG. 2 shows the arrangement of the dressing rings 11 and the
spacer rings 14 in a plan view of the lower polishing pad 4 lying
opposite the polishing pad 3 to be dressed. The spacer rings 14 are
connected to one another by bars 16, which prevent the spacer rings
from executing rotational movements during the dressing of the
polishing pad.
The embodiment according to FIG. 3 differs from the embodiment
according to FIG. 1 essentially in that a single spacer ring 17 is
used as a spacer, which is placed around the inner edge of the
lower polishing pad 4 and around the inner drive gear 6. The spacer
ring 17 has a uniform thickness. The dressing tool in this
embodiment is a dressing ring 18, which is thicker than the
dressing tool of the other embodiment and which therefore has
greater stiffness. The dressing ring 18 bears on the spacer ring 17
in the region of the inner edge of the lower polishing pad 4 and on
the lower polishing pad 4 in the region of the outer edge of the
lower polishing pad 4. Preferably, three such dressing rings 18 are
provided. The distance D.sub.i between the dressing tool 18 (or, in
FIGS. 1 and 2, 11) and the lower polishing pad 4 lying opposite the
polishing pad 3 to be dressed is greater at the inner edge of the
lower polishing pad than the corresponding distance D.sub.o at the
outer edge of the lower polishing pad 4. The difference between the
thicknesses corresponds to the thickness of the spacer ring 17.
FIG. 4 shows the arrangement of the dressing rings 18 in a plan
view of the lower polishing pad 4. The dressing rings 18 bear on
the spacer ring 17 in the region of the inner edge of the lower
polishing pad 4. The spacer ring 17 encloses the inner edge of the
lower polishing pad 4 and the inner drive gear 6.
FIG. 5 shows a sectional representation of the arrangement of
semiconductor wafers 10 during DSP in a gap having a wedge-shaped
profile. The wedge shape of the profile is the result of two
successively performed operations, during which the polishing pads
are dressed in the manner described. The semiconductor wafers lie
in recesses of carriers 8. The carriers have outer teeth 9, which
engage with the inner pin gear 6 and the outer pin gear 7. The
width W.sub.i of the gap at the inner edge of the polishing pads is
greater than the width W.sub.o of the gap at the outer edge of the
polishing pads. The polishing pads are thinner at the inner edge
than at the outer edge. During the DSP, the polishing pads are
rotated in countersense about their rotational axes 5.
While the invention has been illustrated and described in detail in
the drawings and foregoing description, such illustration and
description are to be considered illustrative or exemplary and not
restrictive. It will be understood that changes and modifications
may be made by those of ordinary skill within the scope of the
following claims. In particular, the present invention covers
further embodiments with any combination of features from different
embodiments described above and below.
The terms used in the claims should be construed to have the
broadest reasonable interpretation consistent with the foregoing
description. For example, the use of the article "a" or "the" in
introducing an element should not be interpreted as being exclusive
of a plurality of elements. Likewise, the recitation of "or" should
be interpreted as being inclusive, such that the recitation of "A
or B" is not exclusive of "A and B," unless it is clear from the
context or the foregoing description that only one of A and B is
intended. Further, the recitation of "at least one of A, B and C"
should be interpreted as one or more of a group of elements
consisting of A, B and C, and should not be interpreted as
requiring at least one of each of the listed elements A, B and C,
regardless of whether A, B and C are related as categories or
otherwise. Moreover, the recitation of "A, B and/or C" or "at least
one of A, B or C" should be interpreted as including any singular
entity from the listed elements, e.g., A, any subset from the
listed elements, e.g., A and B, or the entire list of elements A, B
and C.
* * * * *